1. Field of the Invention
The invention relates to an electronic weighing apparatus with a load pan, a load receiver which is part of a parallel construction and supports the pan, and at least one two-armed force-transmitting lever with a shorter arm which takes up the force transmitted by the load pan, and a longer arm for the balancing force, and finally with a built-in calibrating device.
2. Prior Art
In order to permit regular sensitivity testing in electronic weighers, which e.g. seems indicated in weighers with a high reduction ratio and in gauged weighers, installation of a calibrating device is suitable. Calibrating is thereby simplified and errors caused by a possibly improper storage of an external calibration weight piece are avoided.
To this end, it has been suggested (DE-GM 7607012) to lengthen the shorter arm of the two-armed force-transmitting lever and to provide thereon a support for a calibration weight piece that can be lowered. This suggested structure, however, entails the disadvantage that the shorter arm of the two-armed force-transmitting lever must be lengthened approximately to the length of the longer arm of this lever, in order to obtain for the calibration weight piece the same force-transmitting factor as for the system for the generation of the balancing force. This requires more space and significantly increases the inertia moment of the two-armed force-transmitting lever, whereby the building-up time of the weigher becomes longer. It is also conceivable to modify this structure in such a way that the calibration weight piece is arranged on the longer arm of the two-armed force-transmitting lever. However, due to the force direction reversal of the two-armed lever, this produces the result that the calibration weight piece must in normal operation rest against its support and be lifted only for calibration. This again increases the moment of inertia of the two-armed force-transmitting lever during the normal weighing operation, so that in this case, too, a longer building-up time results. Moreover, the increased lever mass leads to greater problems in the transportation safety of the weighing apparatus.
Furthermore, it is known from U.S. Pat. No. 4,156,361 to provide in an electronic weigher with parallel construction a calibration weight piece below the weighing pan and to lower it to a hanger attachment for calibration. This arrangement, is very well suited to small maximum loads, but for weighing ranges from some kilogram maximum load upward, which loads are customary for weighers with force-transmitting levers, it leads to very heavy calibration weight pieces, which makes the weigher correspondingly heavy, bulky, and expensive.